Using a dynamic gas journal bearing in a free-piston Stirling convertor requires an analysis of the bearing which takes into account the actual working conditions of the bearing with high surrounding pressure, different boundary pressures on the bearing edges and axial movement of the “shaft”. Such an analysis has been developed and provides the steady state and dynamic characteristics of the gas bearing. Based upon this analysis a FORTRAN code has been written which, in addition, may be used to determine the influence of thermal, mechanical and manufacturing distortion.
A generic bearing typical of one used in a 25 kW Stirling convertor was analyzed. The reported steady-state performance includes the load capacity, the power lost in friction and the axial flow. The dynamic analysis establishes the stability criteria of the gas lubricant film.
The bearing radial clearance has a strong influence on the load capacity and axial flow past of the bearing. This influence can be used to optimize the bearing clearance with respect to the bearing efficiency and manufacturing possibilities. The pressure difference at the bearing edges and the axial movement of the shaft have negligible influence on the bearing performance. A perfect cylindrical bearing runs with whirl motion but could be accept. Any distortion, in the bearing radial clearance, can improve the bearing performance. A waved bearing concept has been shown to improve both the steady-state and the dynamic performance.